Lectins are a group of carbohydrate-binding proteins capable of recognizing specific carbohydrate structures and widely distributed in living organisms. Animal lectins are classified into various families according to their sequence similarities in carbohydrate-recognition domains (CRDs) and sugar-binding specificities. They play roles in a variety of physiological processes, functioning as cell surface receptors, involving in interactions between cells during development and differentiation or taking part in recognition of foreign molecules during immune responses. In recent years, biochemical and physiological properties of humoral lectins from marine resources have been thoroughly investigated. Lectins from marine organism such as plasma lectins from Horseshoe crab can recognize lipopolysaccharide (LPS). LPS typically consists of a hydrophobic domain known as lipid A (or endotoxin), a nonrepeating “core” oligosaccharide, and a distal polysaccharide (or O-antigen). BRL, a bacteria-recognizing and LPS-binding protein, is a hemolymph protein isolated from Tachypleus tridentatus in Taiwan. BRL shows a 68% sequence identity with tachylectin-3, a lectin isolated from the amebocytes of Japanese T. tridentatus. Native BRL isolated from hemolymph is capable of binding to three species of bacteria, Streptococcus pneumoniae R36A (Gram-positive), Vibrio parahaemolyticus (Gram-negative), and Escherichia coli Bos-12 (Gram-negative) in a dose-dependent and saturable manner. Native BRL purified from the plasma of Taiwanese T. tridentatus was consisted of different glycosylated and partially-protease-cleaved forms which caused difficulties in determining the exact moiety possessing bacterial binding activity. Since horseshoe crab is an ancient marine arthropod and isolation of native BRL directly from hemolymph does not conform to humanism, recombinant BRL (rBRL) has been engineered and expressed by a yeast strain P. pastoris KM71. However, the reported expression of glycosylated BRL in P. pastoris KM71 was low, as only about 0.6 mg of purified BRL from 500 ml of culture medium could be obtained by LPS-Sepharose CL-4B column chromatography.
Endotoxin detection and removal have large market in drug companies. Global pharmaceutical diagnosis market continues to grow annually. However, current diagnoses of pathogens heavily rely on conventional bacteria culture and colony counting methods which are labor- and time-consuming. For pathogenic bacteria inhibition, antibiotics are potent antibacterial agents with high specificity. However, the relentless emergence of antibiotic-resistant strains of pathogens, together with the retarded discovery of novel antibacterial agents has led to the need to find alternative treatments. Development of new strategies for pathogenic bacteria detection and treatment is required.